Immunoassay, especially radioimmunoassay (RIA), is the most widely used diagnostic tool in biomedical laboratories. In recent years, it application began to spread to such diverse areas as environmental health, veterinary science, agriculture, food industry, etc. Concommitant with the expanding market, however, there has been increasing constraints on the usage of RIA due to the biological hazards of radioisotopes. Similar to other attempts in seeking an alternative method, we introduced a nonradioactive immunoassay--ferritin-linked immunoassay (FLIA). During Phase I, we have established that FLIA, in which the antigen is labeled with an iron containing protein--ferritin, can be a better candidate to replace RIA. Thus, during Phase II, we plan to: (A) simplify the procedure by replacing the double-antibody method with a solid phase method, (B) upgrade the colorimetric method of iron detection by substituting the ferrozine method with the chromazurol method, and (C) test an alternative, more sensitive method of iron analysis--the coulometric method. In addition, we plan to develop tow biomedically useful prototype FLIA systems for (A) beta-human chorionic gonadotropin, and (B) prostaglandins. Upon completion of these aims, we will be more than ready to transform these research findings into commercial productions.